Oxidative regeneration method

ABSTRACT

Process and apparatus for recovering and regenerating spent manganese oxidant in an aqueous stream by concentrating the spent oxidant to produce a thickened slurry, forming a charge of freeflowing granular particles from the slurry and oxidizing the charge. The stream may be thickened by employing a settling tank, formed into a charge in a solids mixer, and oxidized in a regeneration dryer.

9 Matted States Patent [151 3,653,824 Barker et al. 51 Apr. 4, 1972 54]OXIDATIVE REGENERATION METHOD 3,470,061 7/1969 Barker ..23/134 [72]Inventors: Richard G. Barker, Princeton Junction, OTHER PUBLICATIONSN.J.; James L. Ma, Los Angeles, Calif.

Chemical Engmeenng, Jan. 1954, Vol. 61, p. 372- 375 {731 Assignee: UnionCamp Corporation, New York,

N -Y- Primary Examiner--Oscar R. Vertiz Assistant Examiner-Hoke S.Miller [22] Filed" 1969 AttorneyKane, Dalsimer, Kane, Sullivan andKurucz [21] Appl. No.2 867,057

[57] ABSTRACT {52] us. Cl ..23/145 Process and apparatus for ring nregenerating spent [5 1 1 Int (3| I I 0 45/02 manganese oxidant in anaqueous stream by concentrating the 581 Field of Search ..23/145, 135,285 p oxidant to Produce a thickened Slurry, forming a charge offree-flowing granular particles from the slurry and oxidizing I 56]References Cited the charge. The stream may be thickened by employing asettling tank, formed into a charge in a solids mixer, and oxidizedUNITED STATES PATENTS in a Fegeneration y 3,4l8,237 12/1968 Booth et a]...23/134 11 Claims, 1 Drawing Figure DEVEE M/XEE #74752 i 7 I I 22 I- 26J A I I e L l 1 I I 2 l l I l I I I 4 *6 24 I 1 I I l I #7257" I l zgarae ff/VGE l l I DA=/ I I e I l 5 I l I 7 I c L I I I I 7 A2 Alfie i IPvu-rzmv; I I I f mm, F/LfE I I I L T J I I I l c l I l BACKGROUND CFTHE INVENTION The term manganese oxidant, as employed herein, is definedas a mixture of a major portion of manganese oxides wherein themanganese is in higher oxidation states and greater than 2 and usuallysuch higher manganese oxides as MnO MnOOH, Mn O.,, Mn O and a minorportion of manganese oxides wherein the manganese is in lower oxidationstates and no greater than 2 and including a substantial portion ofmanganous oxide.

Spent manganese oxidant is defined as a mixture of a major portion ofmanganese oxides, wherein the manganese is in lower oxidation states andno greater than 2 and including a substantial portion of manganousoxide, and a minor portion of manganese oxides, wherein the manganese isin higher oxidation states and greater than 2 and generally MnO MnOOI-I,Mn O,,, and Mn O The invention relates to a process and apparatus forrecovering and regenerating spent manganese oxidant discharged from anoxidizer. In particular, it relates to a process and apparatus forproducing more uniform size controlled manganese oxidant particles fromspent manganese oxidant discharged from a reactor in which sulfides,present in an alkaline pulping liquor system are converted topolysulfide sulfur.

In Barker US Pat. No. 3,470,061, a process is disclosed for generatingsodium polysulfide sulfur from sodium sulfide pulping liquors byemploying an insoluble, oxidizing manganese compound. The teachings ofthe Barker patent are expressly incorporated by reference into thepresent application. The Barker patent discloses that spent manganeseoxidant may be regenerated and recycled for further oxidation ofadditional sulfide.

During the continuous recycling of manganese oxidant in the aforesaidprocess, certain quantities of fines and lumps of manganese oxidant andspent manganese oxidant are produced. Fines are not as susceptible torecovery procedures as larger oxidant particles. Lumpy granules tend tointerfere with the free flow of effluent streams in the pipes andoutlets of a recovery and regeneration system. Generally, largerparticles of oxidant require additional agitation in the reactor inorder to ensure complete commingling with the reactor slurry containingsulfides.

SUMMARY OF THE INVENTION It is, therefore, a primary object of thisinvention to provide an improved process and apparatus for oxidativelyregenerating spent manganese oxidant, particularly in an alkalinepulping liquor-sulfide oxidation process. It is another object of thisinvention to provide a more balanced size distribution of manganeseoxidant particle than has been heretofore liquor oxidation of sulfide topolysulfide sulfur.

The above and other objects are met by concentrating the product streamdischarged from a reactor, wherein manganese oxidant is employed foroxidation purposes and is reduced to lower manganese oxides, to producea thickened aqueous slurry of spent manganese oxidant. In general theslurry contains about 40 percent solids on a weight basis. An effluentproduct stream produced by the concentrating step is separated from theslurry. A settling tank may be employed for this purpose.

The thickened slurry is formed into a granular charge of free-flowingparticles. The moisture content of the particles should be less than 30percent and preferably less than 20 percent by weight, based on totalparticle weight. Should the moisture content of the particles besignificantly greater than the aforesaid, then an undesirablethixotropic mix may be formed. Such a mix cannot be properly regeneratedaccording to the invention. A free-flowing charge may be formed bycombining the thickened slurry with dry material, such as fresh orregenerated manganese oxidant in a solids mixer.

The charge is thereafter oxidized to higher manganese oxides. It ispreferred to oxidize under conditions sufficient to heat the charge to asurface temperature of at least about 200 F. Rotary kiln dryers areparticularly suited for this purpose.

Heretofore, the fresh, initial oxidant charge of uniform particle sizeprepared by conventional techniques had deteriorated and broken downduring continuous processing. It is an important feature of theinvention that the regenerated oxidant is maintained in a more balancedand uniform particle size distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although applicabletootherprocesses employing manganese oxidant the invention is preferablyemployed in a conventional alkaline pulping liquor system, and mostpreferably in a kraft liquor pulping process. Typically, manganeseoxidant is employed to convert sulfides in kraft pulping liquor topolysulfide sulfur.

This reaction is carried out in a well-stirred reactor, employing kraftliquor. Reactants are agitated in the reactor to keep the oxidant ingood contact with the white liquor. The degree of agitation required forparticle suspension is dependent, in part, on the particle size of theoxidant. As the size of the oxidant particles in the reactor increases,a greater degree of agitation is required to keep the particles insuspension.

Generally, the rate of manganese oxidant addition is adjusted close tothe stoichiometric requirement of 1 mole of manganese dioxide for eachmole of sodium sulfide in the white liquor. The concentration of oxidantmay be up to 60 percent by weight, but is preferably from 5 to 20percent by weight, based on the total weight of the mix. The reaction isgenerally carried out in less than about 2 hours and preferably in fromabout 15 to 45 minutes, although, depending on the temperature employedand degree of agitation of the mixture, the reaction may be carried outfor up to about 8 hours.

The temperature of the reaction mix may be from about 70 to 300 F. Attemperatures above the boiling point of the mixture, pressure must beapplied to the mix to prevent undesirable, uncontrolled boiling. Thismay be accomplished simply by employing a closed reaction vessel. Thepreferred reaction temperature is from about to F. For present purposes,the pH of the mix is preferably alkaline.

The degree of sulfidity of the mix is at least about 15 percent and ispreferably at least about 25 percent.

The product stream discharged from the reactor contains typically,polysulfide sulfur, a strong inorganic base, spent manganese oxidant,and water, among other constituents.

To recover and regenerate the spent manganese oxidant in this stream,the spent oxidant is first concentrated and separated from thepolysulfide sulfur and other dissolved or liquid constituents. This maybe accomplished by performing one or more of the following steps and/orcombinations thereof: flocculating, settling, centrifuging, wetcycloning and the like. In general, it is preferred to form a thickenedaqueous slurry of spent oxidant havinga solids concentration of fromabout 40 to 60 percent by weight, based on the total slurry weight.

In one embodiment, the product discharge stream is concentrated to aslurry having about 40 percent by weight spent oxidant solids. Asettling tank, centrifuge and the like, and/or flocculants may beemployed for this purpose. The overflow effluent is separated byconventional techniques. The thickened slurry is then partially driedemploying conventional dryers to a solids content of at least about 70percent and preferably 80 percent by weight. The partially dried mass isthen crushed to form a free-flowing granular charge, which is treatedaccording to the invention herein disclosed. A roll crusher may beutilized for this operation.

In a second and more preferred embodiment, the reactor discharge streamis concentrated to 40 percent by weight solids content and morepreferably from 40 to 60 percent solids by weight, and the liquideffluent is separated as set forth heretofore. This step may also beefiected by adding flocculant to the stream and thereafter settling thestream in a tank equipped with a compacting rake. The thickened slurryof spent oxidant is introduced into a solids mixer for conversion into afree-flowing granular charge by means described below.

In a third and most preferred embodiment, the effluent stream isinitially flocculated employing mechanical and/or chemical flocculationtechniques. Enhanced results are obtained, however, when a flocculatingagent is introduced into the reactor discharge stream near the dischargeend of the reactor and the flocculated effluent stream is thereaftersettled to produce a thickened aqueous slurry of spent manganeseoxidant.

The flocculating agent employed must be stable in the basic (caustic)effluent stream. Suitable agents include anionic and non-ionicflocculants. The flocculants may be organic or inorganic. Typicalnon-ionic flocculating agents include: polyethylene glycols, polyvinylalcohols, polyethers, and polyesters. Examples of typical non-ionicflocculants include: polyoxyalkylene derivatives of sorbitan monooleate,sorbitan trioleate, sorbitan monostearate, sorbitan palmitate, sorbitanmonolaurate, and sorbitan oleate, and polyethylene glycol distearate.Preferred non-ionic flocculants include polyacrylamides having molecularweights of from about 1 million to 6 million. Particularly preferredflocculants are Dow Chemical NP20, a non-ionic polyacrylamide with amolecular weight in excess of 1 million, Dow Chemical MGL, a non-ionicpolyacrylamide with a molecular weight of about 1 million and StandardBrands-Tylac a non-ionic polyacrylamide with a molecular weight of about6 million.

Typical anionic flocculants include carboxylates, as sodium oleate andsodium palmitate, sulfates and sulfonates, particularly metal alkarylsulfonates. Especially preferred anionic flocculating agents includesodium polystyrene sulfonate and causticized starch. Causticized starchmay be prepared by mixing one-half part cornstarch and one-half partsodium hydroxide pellets per 100 parts of water.

Generally, in the case of non-ionic flocculants, and, particularly forthe preferred polyacrylamides, 30 to 60 ppm flocculant is employed inthe discharge stream from the reactor, based on the total solids contentof the stream. The flocculants are preferably added to the effluentstream as a dilute aqueous solution. The preferred concentration offlocculant in said solution is from about 0.05 to 0.10 percent byweight, based on the total weight of the solution.

In the case of the anionic flocculants, sufficient quantities areemployed to allow a residence timeof no longer than about 2 hours whenemploying a suitable settling tank. When causticized starch is employed,up to 2,000 ppm can be added. Enhanced results are obtained when fromabout 200 to 1,500 ppm are employed.

The flocculated effluent stream is thereafter preferably treated bysettling in a settling tank. The tank is preferably provided with ameans for compacting the particles which collect at the bottom of thetank. A compacting rake is suitably employed. A concentrated slurrywhich forms at the bottom of the settling tank is generally from about30 to 60 percent solids, as compared to the 5 to 20 percent solidsnormally found in an unfiocculated effluent stream. Depending on theparticular flocculants employed and the efficiency of the settling tank,among other factors, an effluent stream discharged from the settlingtank may contain anywhere from about less than 30 to greater than about200 ppm solids.

It is preferred that the residence time of the non-ionic flocculatedeffluent stream in the settling tank be at least about 2 hours. Ifdesired, one may heat the reaction slurry within the settling tank inorder to induce more rapid settling. However, much care should be takenin order to avoid producing a thermal gradient therein, which would tendto inhibit settling.

In order to further reduce the solids content of the efiluent streamdischarged from the settling tank, various filters may be employed. Itis preferred to employ a polishing filter. If the solids content of theeffluent stream from the settler is less than about 50 ppm, thepolishing filter need not be employed. The spent oxidant cake built upin such a filter may be back flushed and returned to either the settlingtank or to the reactor wherein sulfides are oxidized to polysulfide orto any other convenient point in the process.

It is particularly preferred to form a chargeof free-flowing granularparticles from the concentrated slurry of the settler, said particleshaving a moisture content of less than about 20 percent, by employing incombination, a vacuum belt filter and a solids mixer. The thickenedslurry, containing from about 40 to 60 percent solids is transportedfrom the settler to the vacuum filter wherein a cake containing at leastabout 60 percent by weight solids is produced. If the filter cake hasless than about 60 percent by weight solids, the cake will tend to stickto the belt.

It is particularly preferred to employ a top-loading horizontal vacuumbelt filter utilizing a vacuum from about 10 to 20 inches of mercury. Ifa higher vacuum is employed, there is a danger of flashing the filtrate.It is preferable to wash the belt filter cloth between removal of thecake and additional filtration in order to prevent the product fromblinding the filter cloth. The washing material may be the productstream from the polishing filter or the white liquor from the inletfeed.

A thickened slurry or filter cake of spent oxidant, generallythixotropic in nature, may be converted to a free-flowing granularcharge by adding substantially dry manganese oxide particles thereto andcombining said dry particles with said cake in a solids mixer.Generally, it is preferred to employ regenerated manganese oxidanthaving a moisture content below about 5 percent by weight for thispurpose. In addition, fresh manganese dioxide particles may also beemployed in order to replace oxidant lost in the process, if any.However, the fresh manganese dioxide particles may be added at otherpoints in the recovery and regeneration process. From 3 to 1 parts drysolids per part wet solids are used.

After the dried manganese oxide solids are added to the thixotropicmass, it is passed through a sigma mixer, or, more preferably, adouble-shafted pug mill mixer to produce a freeflowing granular charge.

This charge should preferably have a moisture content of less than about30 percent by weight and, most preferably, less than about 20 percent byweight in order to expedite proper and efficient regeneration. If thecharge is too moist prior to regeneration, it forms hard lumpyaggregates during regeneration. These aggregates tend to oxidize slowlyand unevenly, thus reducing the efficiency of the invention. Generally,the charge for the regenerator contains about 25 percent by weightmanganese dioxide (employing conventional oxalate analysis) and based ontotal solids, as supplied, primarily by regenerated add-back manganeseoxidant and any fresh makeup manganese dioxide added to make up systemloses.

Next, the charge is oxidized. Generally, a regeneration dryer isemployed. The temperatures in the dryer should be sufiicient to reducethe moisture content of the granules to less than about 30 percent byweight and more preferably to less than about 10 percent by weight.Below about 10 percent by weight moisture, the surface temperature ofthe particles tends to rise especially rapidly during heating, therebyexpediting oxidation.

Generally, a stoichiometric excess of oxygen is present within the dryerin order to convert the charge to a sufiiciently regenerated manganeseoxidant. Suitable gases for this purpose include oxygen and oxygeneousgases, containing from 5 to percent oxygen. For most purposes, gases,and particularly air, employed in the dryer contain from about 15 to 21percent by volume oxygen. Regeneration of the particles preferably takesplace in the presence of a strong base, preferably sodium hydroxide. Thebase may be added after the product stream is discharged from thereactor, if desired.

The temperature of the gases within the dryer is maintained at fromabout ambient temperature to about l,500 F. A preferred workabletemperature range for the gas is from about to 600 F.

Various conventional dryers such as batch and continuous dryers, forexample, fluidized bed dryers, rotary dryem, and tunnel dryers areutilized. It isnormally preferred to employ a rotary kiln regenerationdryer having a top feeder. In the dryer the flow of heated oxidizing gasis preferably directed countercurrent to the manganese oxidant in orderto avoid dusting problems. The residence time for the charge in theregeneration dryer is from about A to 1 hour.

By employing the previously stated air temperatures and residence time,a regenerated manganese oxidant is obtained, having from about 30 to 45percent by weight manganese dioxide based on oxalate analysis. Higherconcentrations of manganese dioxide are obtained by employing longerresidence times and/or employing higher concentrations of freshmanganese dioxide particles in the charge conveyed into the regenerationdryer. The regenerated manganese oxidant particles obtained oncontinuous recycling are of more balanced and optimum particle sizedistribution than produced heretofore. A substantial portion of theparticles, and usually over 50 percent are greater than about 325 mesh.Such particle size control reduces the amount of fines which can be lostto the product stream.

To insure that unduly large manganese oxidant particles are notintroduced into the reactor, a roll crusher is optionally employed. Theroll crusher breaks up a portion of the large particles and over about100 mesh in size, if formed, from the dryer. For this purpose, the rollsof the crusher are aligned less than about three-eighths of an inchapart and preferably about one-eighth of an inch apart. Steel rolls aresuitable for this purpose.

The further improved recovery and regeneration process of the presentinvention achieves greater recoveries of spent manganese oxidant fromthe effluent stream of the reactor than heretofore obtained. Thefiltration requirements of the polysulfide sulfur stream discharged fromthe reactor is reduced to a point not achieved heretofore. Stronger andmore uniform manganese oxidant particles are regenerated which resistthe disintegrating forces present in the overall system.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing depicts a flowsheet illustrating preferred embodiments of the invention.

Referring now to the flow sheet, an alkaline pulping liquor streamcontaining sulfides A is introduced into reactor wherein the sulfidesare oxidized to polysulfide sulfur by manganese oxidant. Product streamB containing spent oxidant is discharged from the reactor. Flocculantmay be added to such stream, as shown at C.

The stream is introduced into a thickener 12 wherein a concentratedslurry of spent manganese oxidant and an effluent stream D containingpolysulfide sulfur, among other constituents, is produced. Theconcentrated slurry is discharged from the thickener and may beintroduced onto a vacuum belt filter 14. The settling tank effluent isintroduced into a polishing filter 20.

The effluent discharge from the polishing filter is circulated toconventional alkaline pulping liquor processing system F. A portion ofthis efiluent H is employed to wash the vacuum belt filter to preventblinding thereof.

To the filter cake discharge from vacuum filter 14 there is added freshmanganese dioxide E and regenerated manganese oxidant G. The mixture isthereafter introduced into solids mixer 16 for conversion into afree-flowing granular charge. The charge is conducted from the solidsmixer 16 to a regeneration dryer 18. After a regenerated manganeseoxidant charge has been formed in dryer 18, it is thereafter dischargedand passed between rolls 22 of a roll crusher.

As illustrated in the drawing, fresh manganese dioxide may be added tothe oxidant stream at any convenient place in the system. Asillustrated, the manganese dioxide could be added at point I after theroll crushers 22 rather than at point E, after filter 14.

If desired, white pulping liquor may be employed in conjunction with orin place of effluent H for washing the vacuum belt filter.

In another embodiment of the invention, the thickened slurry isconducted to a first stage dryer 24 wherein the slurry is partiallydried. From dryer 24 the partially dried oxidant is conducted throughthe rolls of crusher 26 to form a free-flowing granular charge. From thecrusher the charge is introduced into dryer 18.

In a third embodiment, the thickened slurry J is admixed with freshmanganese oxidant E and regenerated manganese oxidant G and conducted tosolids mixer 16 for conversion into a free-flowing charge.

Although the pulping liquor introduced into the reactor may contain astrong base, such base may also be added at a convenient point in therecovery and regeneration process, for example at K.

The following examples are given to illustrate the invention and are notlimitative of scope.

EXAMPLE I In the following two continuous runs, kraft white liquorcontaining alkali was introduced into a stirred reactor tank along withmanganese oxidant. The reactor product stream containing spent oxidantwas discharged and mixed with a flocculating agent. Thereafter thestream was settled in a thickenerclarifier tank. The effluent wasintroduced into a polishing filter. The thickened slurry produced in thethickener was conducted to a vacuum filter extractor having a beltconveyor and was washed with polishing filter effluent liquor. Thefilter cake continuously produced was introduced into a pug mill solidsmixer and regenerated oxidant was added thereto.

The free-flowing charge from the solids mixer was fed into a tunneldryer employing air for regeneration. From the dryer, the regeneratedoxidant was passed between the rolls of a roll crusher. The solidsdischarged from each of the apparatus employed herein were sampled andanalyzed and are reported below:

The following table illustrates the parameters employed at the variousstages of the aforesaid process:

Run l Run 2 l. REACTOR Agitator speed, in RPM 226 226 White Liquor in:

a. Rate of introduction,

gallons per minute 1.0 L0 b. Sulfidity, 27.0 24.7 Oxidant addition rate,pounds per minute L22 1.63 Temperature, F. I75 Residence time of batchin reactor, hrs. 2.0 2.0 Sodium Sulfide in grams/liter 35.5 32.0 2.REACTOR OXIDATION PRODUCTS DISCHARGE STREAM Solids Concentration, wt.12.0 16.0 Polysulfide, grams/liter 7.5 7.0 Sodium Sulfide, grams/liter[5.1 11.5 Flocculant added polyacrylsodium amide polystyrene sulfonateConcentration of flocculant in water prior to addition, 5% wt. 0.05 0.05Dosage level fiocculant in Product Stream, PPM 30 60 3.THICKENER-CLARIFIER Residence Time therein, hrs. 4.3 4.3 Compacting RakeSpeed, rpm. 3.5 3.5 Solids in underflow (slurry) wt. 30 36 Solids inoverflow (effluent) ppm 64.0 35.2 4. POLISHING FILTER Oxidant particlesin polished product liquor, ppm 2.9 2.9 5. VACUUM FILTER-EXTRACTORSolids in Filter Cake formed,

it by weight 76 75 Vacuum, in inches mercury I Manganese Dioxide inCake,

2 by wt. l7.4 17.2 6. SOLIDS MIXER Solids added to filter cake, 1:solids in add-back by wt. 90.0 97.4 Solids in free-flowing chargeproduced, it by wt. 83.5 87 Ratio of added solids to cake solids 1.361.1 7. TUNNEL DRYER Air temperature, F. 320 320 Air Rate, Cu. FtJmin.400 400 Residence Time of charge in dryer, min. 3O 30 Manganese Dioxideat exit, dryer, by wt. 36.4 33.5 Solids in charge, after regeneration,wt. 95.2 93.0 8. ROLL CRUSHER Roll gap, inches 0.090 0.112

The above table illustrates the'effectiveness of the invention. Theconcentration of manganese dioxide in the spent oxidant is 17.4 percentas analyzed by the direct oxalate method (see run 1 at vacuum filter).The concentration of manganese dioxide in the regenerated oxidant is36.4 percent as analyzed the direct method followed after thoroughwashing in oxygenfree atmosphere is given in Standard Methods ofAnalysis, 6th Ed., N. H. Furman editor, Vol. I, p. 778, (see run 1 attunnel dryer).

The following table illustrates the change in particle distribution ofspent oxidant as it flows through the inventive system from the reactorproduct stream and through the roll crusher prior to introduction intothe reactor. The table shows the weight percentage of particles over 100mesh, between 100 and 325 mesh, and less than mesh in size in theoxidant for two runs at various points in the process.

SIZE DISTRIBUTION OF PARTICLES l00 Mesh l00 325 325 Mesh Product StreamRun l Run 1 Run I From Reactor 7.2 15.3 77.5 (wt. k of particles) Run 2Run 2 Run 2 Discharge From Run l Run 1 Run l Thickener 7.2 35.6 58.2

Run 2 Run 2 Run 2 Discharge From Run l Run l Run 1 Polish Filter 0 11 89Run 2 Run 2 Run 2 Discharge From Run 1 Run 1 Run l Solids Mixer 23.]16.2 60.7

Run 2 Run 2 Run 2 Discharge From Run 1 Run 1 Run l Dryer 55.2 18.3 26.5

Run 2 Run 2 Run 2 Roll Crusher Run l Run 1 Run I 27.4 27.6 44.7 Run 2Run 2 Run 2 The size distribution of particles of oxidant is markedlyaltered by the invention. In run I, for example 77.5 percent of theparticles from the reactor were less than 325 mesh. After regeneration,only 44.7 percent of the particles were less than 325 mesh. Also, only22.5 percent of the particles from the reactor were greater than 325mesh, as contrasted to the 55 percent greater than 325 mesh dischargedfrom the roll crusher after regeneration.

From the runs illustrated above, it is seen that the regenerationprocess provides greater than 100 percent increase in availablemanganese dioxide as compared to the spent oxidant stream dischargedfrom the reactor. Further, it should be noted that the concentration ofsolids in the oxidant is increased eightfold over the solidsconcentration in the reactor discharge. Significantly, the particle sizedistribution of the regenerated oxidant is markedly readjusted by theprocess to reduce the quantity of very small particles (less than 325mesh), in the reactor oxidant charge. A I00 percent increase is noted inthe size of particles greater than 325 mesh.

EXAMPLE II A white liquor stream containing sulfides is admixed withmanganese oxidant according to the procedure of Example I with theexception of the following parameters:

1 Reactor Temperature F. 2 l0 Residence Time, min. 2. Reactor DischargeStream Solids, concentration it,

by wt. 4

Flocculant employed causticized starch Dosage Level flocculant,

ppm 1000 MnO in Stream, 20

by weight as calculated by the direct oxalate method 3. ThickenerClarifier Solids in underflow Solids in overflow, ppm 20 4. VacuumFilter-Extractor Solids in filter cake formed, wt. 60

5. Solids Mixer Solids in charge produced, wt. 30

6. Tunnel Dryer Gas Temperature, F. l50

Oxygen in gas, '7: vol.

The oxidant charge produced contains 30 percent by weight manganesedioxide by oxalate analysis and the solids content of the charge is 90percent by weight.

EXAMPLE III eliminating the use of the vacuum filter:

2. Reactor Discharge Stream Solids, wt. 1: 40

Flocculant employed sodium polystyrene sulfonate MnO, in Stream, k

by weight as 5 calculated by the direct oxalate method 3.Thickener-Clarifier Solids in underflow,

wt. 7: 5O

Solids in overflow,

PP 200 4. Solids Mixer Solids in charge, Z: wt. 75 5. Tunnel Dryer Gastemperature, "F. I000 The oxidized charge produced, contains 42 percentby weight manganese dioxide as analyzed and the solids content of thecharge is 99 percent by weight.

Examples II and III illustrate the capabilities of the process andapparatus of the invention as temperatures, flocculant, residence time,and apparatus are varied within process limits. Further combinations andembodiments will be obvious to those skilled in the art, such ascentrifuging the product slurry and directing the slurry to the solidsmixer and the like.

Wherefore I claim:

1. In a process employing manganese oxidant for oxidation purposes in areactor including the steps of producing an aqueous product streamcontaining spent manganese oxidant, wherein a major portion of manganeseis said spent oxidant is in lower oxidation states, producing athickened aqueous slurry of spent manganese oxidant, air-oxidizing thespent oxidant to form a regenerated manganese oxidant wherein a majorportion of the manganese in the regenerated oxidant is in higheroxidation states and reusing the regenerated oxidant for oxidationpurposes, the improvement which comprises:

forming a charge of free-flowing granular particles from said slurryprior to oxidizing the slurry, whereby the particles are reoxidized intoa hardened particulate manganese oxidant charge wherein a major portionof said hardened particles are of a size greater than that passingthrough a number 325 mesh screen, thus reducing the tendency of saidspent manganese oxidant to form into fines and lumpy aggregates duringregeneration.

2. The process of claim 1 in which the solids content of thefree-flowing particles at least are about 70 percent by weight.

3. In a process of oxidizing sulfide to polysulfide sulfur by reactionwith manganese oxidant in a reactor associated with an alkaline pulpingsystem including the steps of producing an aqueous product streamcontaining spent manganese oxidant wherein a major portion of saidmanganese in said spent oxidant is in lower oxidation states, forming athickened aqueous effluent stream; c. formlng a charge of free-flowingparticles from said slurry, said particles having a moisture content nogreater 7 than about 30 percent by weight based on the total weight ofthe particles;

. heating said charge at from about 160 to 600 F. to reoxidize saidcharge such that the moisture content of the particles is reduced toless than about 10 percent by weight and the surface temperature of theparticles reaches at least about 200 F and e. recycling said reoxidizedcharge to said reactor,

whereby the spent manganese oxidant is reoxidized to a hardenedparticulate charge, wherein a major portion of said hardened particlesare of a size greater than that passing through a number 325 meshscreen, thus reducing the tendency of the regenerated oxidant to forminto fines and lumpy aggregates during regeneration.

4. The process of claim 3 in which the slurry is concentrated to atleast about 40 percent solids by weight, and thereafter, the slurry iscombined with sufficient substantially dry manganese oxidant to form afree-flowing granular charge having a moisture content no greater thanabout 20 percent by weight of said charge.

5. The process of claim 3 and in addition the steps of vacuum filteringthe thickened slurry to produce a filter cake having a solids content ofat least about 60 percent by weight manganese oxidant solids andcombining the filter cake with substantially dry manganese oxidant toproduce a charge of free-flowing granular particles having a moisturecontent no greater than about 20 percent by weight.

6. The process of claim 3 and the steps of partially drying thethickened slurry to a charge having a moisture content no greater thanabout 20 percent by weight and thereafter crushing the partially driedslurry to form a free-flowing granular charge suitable for oxidizing.

7. The process of claim 3 and including the step of filtering theeffluent stream produced by the settling step to recover additionalspent manganese oxidant.

8. The process of claim 3 in which the flocculant is a polyacrylamidehaving a molecular weight of from about 1 million to 6 million.

9. The process of claim 3 in which the flocculant is sodium polystyrenesulfonate.

10. The process of claim 3 in which the flocculant is a causticizedstarch.

11. The process of claim 3 including the step of passing said reoxidizedcharge through a crusher prior to said recycling to said reactor toreduce the quantity of particles retained on a mesh screen.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 65324 Dated p il 4 1972 Richard G. Barker et-al.-

Inventor(s) It is certified that error appears 'in the above-identifiedpatent and that said Letters Patent are. hereby corrected as shownbelow:

Column 1., line 55, after "heretofore" insert produced for oxidationprocesses, especially for the kraft Column 7, line 25 after "analyzed"insert (see run 1 at tunnel dryer): line 26. "the" should read The lines28 and 29, cancel (see run 1 at tunnel dryer-')"'.-. Column 9 line 56,"of" should read for Signed and sealed this 7th day-of November 1972.

(SEAL) Attest EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM P0-1050 (10-69) USCOMWDC 6037mm.

\Y [LS4 GOVERNMENT PRINTING OFFICE "I69 0-.-3G6-334.

2. The process of claim 1 in which the solids content of thefree-flowing particles at least are about 70 percent by weight.
 3. In aprocess of oxidizing sulfide to polysulfide sulfur by reaction withmanganese oxidant in a reactor associated with an alkaline pulpingsystem including the steps of producing an aqueous product streamcontaining spent manganese oxidant wherein a major portion of saidmanganese in said spent oxidant is in lower oxidation states, forming athickened aqueous slurry of spent oxidant, air-oxidizing the spentoxidant to a regenerated manganese oxidant charge wherein a majorportion of said manganese in said regenerated charge is in higheroxidation states and reusing the regenerated oxidant for furtheroxidation of sulfide, the improvement which comprises: a. introducing aflocculant selected from the group consisting of non-ionic and anionicflocculants stable in basic solution into the reactor product stream; b.settling said flocculated stream to produce a thickened aqueous slurryof spent manganese oxidant solids and an effluent stream; c. forming acharge of free-flowing particles from said slurry, said particles havinga moisture content no greater than about 30 percent by weight based onthe total weight of the particles; d. heating said charge at from about160* to 600* F. to reoxidize said charge such that the moisture contentof the particles is reduced to less than about 10 percent by weight andthe surface temperature of the particles reaches at least about 200* F.,and e. recycling said reoxidized charge to said reactor, whereby thespent manganese oxidant is reoxidized to a hardened particulate charge,wherein a major portion of said hardened particles are of a size greaterthan that passing through a number 325 mesh screen, thus reducing thetendency of the regenerated oxidant to form into fines and lumpyaggregates during regeneration.
 4. The process of claim 3 in which theslurry is concentrated to at least about 40 percent solids by weight,and thereafter, the slurry is combined with sufficient substantially drymanganese oxidant to form a free-flowing granular charge having amoisture content no greater than about 20 percent by weight of saidcharge.
 5. The process of claim 3 and in addition the steps of vacuumfiltering the thickened slurry to produce a filter cake having a solidscontent of at least about 60 percent by weight manganese oxidant solidsand combining the filter cake with substantially dry manganese oxidantto produce a charge of free-flowing granular particles having a moisturecontent no greater than about 20 percent by weight.
 6. The process ofclaim 3 and the steps of partially drying the thickened slurry to acharge having a moisture content no greater than about 20 percent byweight and thereafter crushing the partially dried slurry to form afree-flowing granular charge suitable for oxidizing.
 7. The process ofclaim 3 and including the step of filtering the effluent stream producedby the settling step to recover additional spent manganese oxidant. 8.The process of claim 3 in which the flocculant is a polyacrylamidehaving a molecular weight of from about 1 million to 6 million.
 9. Theprocess of claim 3 in which the flocculant is sodium polystyrenesulfonate.
 10. The process of claim 3 in which the flocculant is acausticized starch.
 11. The process of claim 3 including the step ofpassing said reoxidized charge through a crusher prior to said recyclingto said reactor to reduce the quantity of particles retained on a 100mesh screen.